[TowerTalk] Getting your moneys Worth

K8RI K8RI-on-TowerTalk at tm.net
Fri Jun 1 18:17:48 PDT 2012

A while back I mentioned trying to fit a Han IV into a 25G and not 
wanting to cut a brace.  As the mast will extend about 12' above the top 
of the tower, I did not consider mounting inside the short section with 
the flat top plate to be desirable either.  Sooo... I finally decided to 
mount the rotator externally and run a two section mast down through the 
tower.   That will leave the rotator 20 feet above ground level and 30 
feet below the flat top plate...give or take a tad.  I should be able to 
stand on the roof and work on it.

The rotator will be mounted on a 3/16ths (0.1875" for those working in 
decimal) steel plate with a 2" stub mast out the top and through a 
thrust bearing.  There will be a sprocket on the mast out of the rotator 
and another on the mast running up through the tower with bearings  
above and below the sprockets.  There will be 2 idlers.  As this is 80P 
chain it's 1" between centers for the rollers. The first digit is the 
number of 1/8ths while the second indicates standard (0) chain.  Chain 
comes in 10' lengths and 10' of 80P just fits in one of the larger "IF 
it fits it ships" boxes.

I haven't weighed it but I'd guess that box ran some where between 20 
and 30#

BTW, Thanks to all those who came up with suggestions on locations to 
find parts that were far cheaper than the big supply houses.  10' of 80P 
can run $130  to $140, but through surplus sales in Texas it was (IIRC 
$40 shipped to my door) Those sprockets are massive too.  Problem now, 
other than making the mounting plates for the rotator and bearings is I 
have to ream out the ID of the large sprockets to fit the mast which is 
2" DOM and the ID of the bearings is 2" for an interference fit.  The 
idlers just fit over a 3/4" bolt.

I think the top of the tower in 
http://www.rogerhalstead.com/ham_files/skyhook.htm is driven by 80P 
chain.  The sprocket in the second photo from the top appears to be for 
80P which looks small in comparison and I'm just using a 2" mast. That 
top section is 3 feet across each side.


Roger (K8RI)

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